mysql/example/query_sync.cpp

//
// Copyright (c) 2019-2020 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#include "boost/mysql/connection.hpp"
#include <boost/asio/io_service.hpp>
#include <boost/system/system_error.hpp>
#include <iostream>

/**
 * For this example, we will be using the 'mysql_asio_examples' database.
 * You can get this database by running db_setup.sql.
 * This example assumes you are connecting to a localhost MySQL server.
 *
 * This example uses synchronous functions and handles errors using exceptions.
 */

/**
 * Prints an employee to std::cout. An employee here is a mysql::row,
 * which represents a row returned by a SQL query. You can access the values in
 * the row using row::values(), which returns a vector of mysql::value.
 *
 * mysql::value represents a single value returned by MySQL, and is defined to be
 * a std::variant of all the types MySQL supports.
 *
 * row::values() has the same number of elements as fields are in the SQL query,
 * and in the same order.
 */
void print_employee(const boost::mysql::row& employee)
{
    using boost::mysql::operator<<; // Required for mysql::value objects to be streamable, due to ADL rules
    std::cout << "Employee '"
              << employee.values()[0] << " "                   // first_name (type std::string_view)
              << employee.values()[1] << "' earns "            // last_name  (type std::string_view)
              << employee.values()[2] << " dollars yearly\n";  // salary     (type double)
}

void main_impl(int argc, char** argv)
{
    if (argc != 3)
    {
        std::cerr << "Usage: " << argv[0] << " <username> <password>\n";
        exit(1);
    }

    /**
     * Connection parameters that tell us where and how to connect to the MySQL server.
     * There are two types of parameters:
     *   - TCP-level connection parameters, identifying the host and port to connect to.
     *   - MySQL level parameters: database credentials and schema to use.
     */
    boost::asio::ip::tcp::endpoint ep (
        boost::asio::ip::address_v4::loopback(), // host
        boost::mysql::default_port                         // port
    );
    boost::mysql::connection_params params (
        argv[1],               // username
        argv[2],               // password
        "mysql_asio_examples"  // database to use; leave empty or omit the parameter for no database
    );
    // Note: by default, SSL will be used if the server supports it.
    // connection_params accepts an optional ssl_options argument
    // determining whether to use SSL or not. See ssl_options and ssl_mode
    // documentation for further details on SSL.

    boost::asio::io_context ctx;

    /**
     * Represents a single connection over TCP to a MySQL server.
     * Before being able to use it, you have to connect to the server by:
     *    - Establishing the TCP-level session.
     *    - Authenticating to the MySQL server.
     */
    boost::mysql::tcp_connection conn (ctx);
    conn.next_layer().connect(ep); // next_level() returns a boost::asio::ip::tcp::socket
    conn.handshake(params); // Authenticates to the MySQL server

    /**
     * To issue a SQL query to the database server, use tcp_connection::query, which takes
     * the SQL to be executed as parameter and returns a resultset object.
     *
     * Resultset objects represent the result of a query, in tabular format.
     * They hold metadata describing the fields the resultset holds (in this case, first_name,
     * last_name and salary). To get the actual data, use fetch_one, fetch_many or fetch_all.
     * We will use fetch_all, which returns all the received rows as a std::vector.
     *
     * We will get all employees working for 'High Growth Startup'.
     */
    const char* sql = "SELECT first_name, last_name, salary FROM employee WHERE company_id = 'HGS'";
    boost::mysql::tcp_resultset result = conn.query(sql);

    // Get all the rows in the resultset
    std::vector<boost::mysql::owning_row> employees = result.fetch_all();
    for (const auto& employee: employees)
    {
        print_employee(employee);
    }

    // We can issue any SQL statement, not only SELECTs. In this case, the returned
    // resultset will have no fields and no rows
    sql = "UPDATE employee SET salary = 10000 WHERE first_name = 'Underpaid'";
    result = conn.query(sql);
    assert(result.fields().size() == 0); // fields() returns a vector containing metadata about the query fields

    // Check we have updated our poor intern salary
    result = conn.query("SELECT salary FROM employee WHERE first_name = 'Underpaid'");
    auto rows = result.fetch_all();
    assert(rows.size() == 1);
    [[maybe_unused]] auto salary = std::get<double>(rows[0].values()[0]);
    assert(salary == 10000);
}

int main(int argc, char** argv)
{
    try
    {
        main_impl(argc, argv);
    }
    catch (const boost::system::system_error& err)
    {
        std::cerr << "Error: " << err.what() << ", error code: " << err.code() << std::endl;
        return 1;
    }
    catch (const std::exception& err)
    {
        std::cerr << "Error: " << err.what() << std::endl;
        return 1;
    }
}